1. Field of the Invention
The present invention generally relates a microlithographic process for using radiation sensitive photoresist compositions in the fabrication of integrated circuit devices, and more particularly, to a method for using compositions which are processing aids for controlling the sidewall profiles of structures formed from chemically amplified deep UV photoresist compositions and a structure formed thereby. 2. Discussion of the Related Art
In the fabrication of integrated circuits, the exposure of a photoresist to light and subsequent development to form a relief image are important process steps. The production of high density circuits having sub micron dimensions requires that such formation of relief images be accomplished within close processing tolerances. For example, it is important to control the linewidth of the imaged and developed photoresist so that any deviation from the nominal design linewidth is small, typically less than 10%. Furthermore, it is important to control the sidewall profile of the imaged and developed photoresist so as to obtain relatively vertical and straight sidewalls.
Resist sidewall profile is a very important attribute in a lithographically acceptable photoresist structure. Any degradation in sidewall angle or the presence of a foot or undercut will usually be transferred into the substrate during any subsequent etch step. Although, in certain cases, a foot or undercut may be tolerable when it represents only a small percentage of the overall critical dimension, the resist structure is typically considered unusable if it manifests such undesirable characteristics. As the critical dimension becomes smaller, such as less than about 0.40 .mu.m, the percentage becomes larger and its effect becomes intolerable. As sidewall undercut becomes large in proportion to linewidth, undercut may causes the photoresist structure to fall over in the most extreme cases.
Many factors can affect sidewall profile. For example, interference patterns or standing waves may be caused by reflected light. Other distortions may arise from non-planar coatings of photoresist films or underlying topography. Still other distortions may arise from contact reactions, which are adverse reactions between the photoresist film and the underlying material.
In sub micron lithography, the use of acid amplified resists has become favored due to the high photospeed of such compositions. The use of acid amplified resist compositions is well known in the art. Such resist compositions are especially useful in conjunction with deep UV (about 180 to about 300 nm) exposure tools in view of the high photospeed requirements of such tools. The following references illustrate the state of the pertinent art.
U.S. Pat. No. 4,491,628 to Ito, et al., discloses chemically amplified photoresist compositions comprising a photosensitive acid progenitor and a polymeric component having acid labile groups pendent therefrom, wherein the acid labile groups are tert-butyloxycarbonyloxy groups.
Published patent application no. WO 94/10608 to Brunsvold, et al., discloses chemically amplified photoresist compositions comprising a non-metallic photosensitive acid progenitor, particularly sulfonic acid esters of N-hydroxyimides.
Conley, et al., "Advances in Resist Technology and Processing XI, Proc. SPIE.," 1925, 120 (1994) discloses a negative tone chemically amplified photoresist composition comprising polyhydroxystyrene, tetramethoxymethyl glycouril, and a N-hydroxy sulfonate photosensitive acid progenitor.
Although chemically amplified photoresist compositions are favored for sub micron lithography, many chemically amplified photoresists are adversely affected by the presence of certain chemical species, particularly amines. Hinsberg, et al., have discussed particular examples of adverse reactions with N-methyl pyrrolidone. See, Hinsberg, et al., "Advances in Resist Technology and Processing XI, Proc. SPIE.," 1925, 43 (1994), and references therein. For example, where an acid catalyzed cleavage of an acid labile group is required to render the resist composition differentially soluble, a competing reaction between the photogenerated acid and particular chemical species such as an amine will slow or interrupt the cleavage reaction prior to sufficient cleavage of the acid labile group. In such event, acceptable relief images can not be obtained. The degree of completion of the cleavage reaction varies highly depending upon the remaining, unconsumed acid present in the resist at the commencement of the post exposure bake step. The results of such adverse reactions are often unpredictable.
Where the chemical species which reacts with the chemically amplified photoresist emanates from the underlying material, the adverse reaction is often deemed a contact reaction and may be characterized by the formation of a foot, or alternatively an undercut profile, in the sidewall. In the case of an acid catalyzed, positive tone resist, an undercut profile can result from the presence of excess acid species generated in the region of the undercut, which may arise from either the resist or more often the underlying material. In the case of an acid catalyzed, negative tone resist, the resulting profile includes a foot, which may similarly arise from either the resist or more often the underlying material.
Antireflective underlayer compositions are well known microlithographic processing aids. Films formed from such compositions are often applied to microlithographic substrates prior to the application of a photoresist film to control standing waves and other optical aberrations. However, many antireflective underlayer compositions undergo adverse contact reactions with chemically amplified photoresist compositions.
As a result of the propensity of many chemically amplified photoresist compositions to undergo unwanted contact reactions, it is useful to modify the underlying material to compensate for such adverse contact reactions. Thus, a modified underlayer composition, a corresponding lithographic process for the use thereof, is needed for use with chemically amplified photoresist compositions.